Biocidal compositions and methods of use

ABSTRACT

Provided are biocidal compositions comprising: a hydroxymethyl-substituted phosphorus compound and 2-methyl-1,2-benzisothiazolin-3-one. The compositions are useful for controlling microorganisms in aqueous or water-containing systems.

BACKGROUND

The invention relates generally to biocidal compositions and methods oftheir use for the control of microorganisms in aqueous andwater-containing systems. The compositions comprise ahydroxymethyl-substituted phosphorus compound and2-methyl-1,2-benzisothiazolin-3-one.

Protecting water-containing systems from microbial contamination iscritical to the success of many industrial processes, including oil ornatural gas production operations. In oil and gas operations,microorganism contamination from both aerobic and anaerobic bacteria cancause serious problems such as reservoir souring (mainly caused byanaerobic sulfate-reducing bacteria (SRB)), microbiologically influencedcorrosion (MIC) on metal surfaces of equipment and pipelines, anddegradation of polymer additives.

Biocides are commonly used to control the growth of microorganisms inaqueous and water containing systems. However, not all biocides areeffective against a wide range of microorganisms, particularly when usedat low concentrations. In addition, some biocides do not providemicrobial control over long enough time periods, or alternatively areeffective over long time periods, but not short time periods.

While some of these shortcomings can be overcome through use of largeramounts of the biocide, this option creates its own problems, includingincreased cost, increased waste, and increased likelihood that thebiocide will interfere with the desirable properties of the treatedmedium. In addition, even with use of larger amounts of the biocide,many commercial biocidal compounds cannot provide both short term andlong term effectiveness.

The problem addressed by this invention is the provision of biocidesthat are effective against a wide range of microorganisms, that may beused in reduced amounts so as to be economically and environmentallyattractive, and/or that are effective for both short term and long termcontrol of microorganisms.

STATEMENT OF INVENTION

In one aspect, the invention provides biocidal compositions. Thecompositions are useful for controlling microbial growth in aqueous orwater-containing systems, including for applications in the oil andnatural gas industry. The compositions of the invention comprise:2-methyl-1,2-benzisothiazolin-3-one and tetrakis (hydroxymethyl)phosphonium sulfate in a weight ration from 1:5000 to 1:10000.

In a second aspect, the invention provides a method for controllingmicroorganisms in aqueous or water-containing systems. The methodcomprises treating the system with an effective amount of a biocidalcomposition as described herein.

DETAILED DESCRIPTION

As noted above, the invention provides biocidal compositions and methodsof using them in the control of microorganisms. The compositionscomprise 2-methyl-1,2-benzisothiazolin-3-one and tetrakis(hydroxymethyl) phosphonium sulfate. It has surprisingly been discoveredthat combinations of a hydroxymethyl-substituted phosphorus compound andthe isothiazolinone compound as described herein, at certain weightratios, are synergistic when used for microorganism control in aqueousor water-containing media. That is, the combined materials result inimproved biocidal properties than would otherwise be expected based ontheir individual performance at the particular use-concentration. Theobserved synergy permits reduced amounts of the materials to be used toachieve acceptable biocidal properties.

In addition to exhibiting synergy, the compositions of the invention areeffective at providing both short term (2 hours or less) and long term(14 days or more) control of microorganisms. As a result of theseattributes, the compositions are well suited for use in variousapplications, including in the oil and natural gas industry wherebiocidal agents are needed that are capable of controllingmicroorganisms over both the short and the long term.

For the purposes of this specification, the meaning of “microorganism”includes, but is not limited to, bacteria, fungi, algae, and viruses.The words “control” and “controlling” should be broadly construed toinclude within their meaning, and without being limited thereto,inhibiting the growth or propagation of microorganisms, killingmicroorganisms, disinfection, and/or preservation against microorganismgrowth.

The composition of the invention comprises:2-methyl-1,2-benzisothiazolin-3-one and tetrakis (hydroxymethyl)phosphonium sulfate.

The hydroxymethyl-substituted phosphorus compound for use in theinvention is selected from the group consisting of atetrakis(hydroxymethyl)phosphonium salt, a C₁-C₃ alkyl- or C₂-C₃alkenyl-tris(hydroxymethyl)phosphonium salt, andtris(hydroxymethyl)phosphine. Such compounds are generally availableboth in undissolved form or as aqueous solutions. In one embodiment ofthe invention, the hydroxymethyl-substituted phosphorus compound is atetrakis(hydroxymethyl)-phosphonium salt, such as the chloride,phosphate, or sulfate salt. A preferred compound is tetrakis(hydroxymethyl) phosphonium sulfate (THPS). THPS is available from TheDow Chemical Company as AQUCAR™ THPS 75, a 75 wt % solution in water. Ofcourse, more than one of the recited hydroxymethyl-substitutedphosphorus compounds can be combined for use in the present invention;in such cases, ratios and concentrations are calculated using the totalweight of all hydroxymethyl-substituted phosphorus compounds.

The isothiazolinone compound of the invention is2-methyl-1,2-benzisothiazolin-3-one. 2-Methyl-1,2-benzisothiazolin-3-oneis commercially available or they may be readily prepared by thoseskilled in the art.

In some embodiments, the isothiazolinone compound is2-methyl-1,2-benzisothiazolin-3-one and the weight ratio of thehydroxymethyl-substituted phosphorus compound to the2-methyl-1,2-benzisothiazolin-3-one in the compositions of the inventionis between 10000:1 and 5000:1.

The compositions of the invention may contain additional componentsincluding, but not limited to, surfactants, stabilizers, demulsifier,polymers, and/or additional biocides.

The compositions of the invention are useful for controllingmicroorganisms in aqueous or water-containing systems. In someembodiments, the aqueous or water containing system comprises at least10 weight percent, alternatively at least 20 weight percent,alternatively at least 40 weight percent, alternatively at least 60weight percent, or alternatively at least 80 weight percent of water.Non-limiting examples of aqueous or water containing systems with whichthe inventive compositions may be used to control microorganisms includethose present in oil and natural gas applications. Examples of suchsystems include, but are not limited to, injection and produced water,source water for waterflooding and hydraulic fracturing such as pondwater and holding tank water, functional fluids such as drilling muds,completion or workover fluids, hydrotest fluids, stimulation fluids,packer fluids, and fracturing fluids, oil and gas wells, separation,storage, and transportation systems, oil and gas pipelines, oil and gasvessels, or fuel.

The inventive compositions may also be used for controllingmicroorganisms in other industrial aqueous and watercontaining/contaminated systems, such as cooling water, air washer, heatexchangers, boiler water, pulp and paper mill water, other industrialprocess water, ballast water, wastewater, metalworking fluids, latex,paint, coatings, adhesives, inks, tape joint compounds, pigment,water-based slurries, swimming pool, personal care and householdproducts such as detergent, membrane and filtration systems, toiletbowel, textiles, leather and leather production system, or a system usedtherewith.

In some embodiments, the microorganism being controlled with thecompositions of the invention is anaerobic, such as SRB. In someembodiments, the microorganism being controlled is anaerobic, such asSRB, and the aqueous system contains a reducing agent, such as sulfide.

In some embodiments, the microorganism controlled by the composition ofthe invention is yeast, preferably Candida albican.

A person of ordinary skill in the art can readily determine, withoutundue experimentation, the concentration of the composition that shouldbe used in any particular application. By way of illustration, asuitable actives concentration (total for both thehydroxymethyl-substituted phosphorus compound and the isothiazolinonecompound) is typically between 1 and 2500 ppm, alternatively between 5and 1000 ppm, alternatively between 10 and 500 ppm, or alternativelybetween 50 and 300 ppm, based on the total weight of the aqueous orwater-containing system including the biocides. In some embodiments foroil and gas applications, it is preferred that active concentrations ofthe composition range from about 10 to about 300 ppm by weight,preferably about 30 to 100 ppm, for top side treatment, and from about30 to about 500 ppm, preferably about 50 to about 250 ppm, for downholetreatment.

The components of the inventive compositions can be added to the aqueousor water-containing system separately, or preblended prior to addition.A person of ordinary skill in the art can easily determine theappropriate method of addition. The composition can be used in thesystem with other additives such as, but not limited to, surfactants,ionic/nonionic polymers and scale and corrosion inhibitors, oxygenscavengers, and/or additional biocides.

Unless otherwise indicated, numeric ranges, for instance as in “from 2to 10,” are inclusive of the numbers defining the range (e.g., 2 and10).

Unless otherwise indicated, ratios, percentages, parts, and the like areby weight. The following examples are illustrative of the invention butare not intended to limit its scope. Unless otherwise indicated, ratios,percentages, parts, and the like used herein are by weight.

EXAMPLES

The synergy indexes reported in the following examples are calculatedusing the following equation:

Synergy Index=Ca/CA+Cb/CB

Ca: Concentration of biocide A required to achieve a certain level ofbacterial kill when used in combination with B.

CA: Concentration of biocide A required to achieve a certain level ofbacterial kill when used alone.

Cb: Concentration of biocide B required to achieve a certain level ofbacterial kill when used in combination with A.

CB: Concentration of biocide B required to achieve a certain level ofbacterial kill when used alone.

A synergy index (SI) of 1 indicates additivity, a synergy index of lessthan 1 indicates synergy, and a synergy index greater than 1 indicatesantagonism.

Example 1

Synergistic Effect of Tetrakis (Hydroxymethyl) Phosphonium Sulfate(THPS) and 1,2-Benzisothiazolin-3-One (BIT).

A sterile salt solution (0.2203 g of CaCl₂, 0.1847 g of MgSO₄, and0.2033 g of NaHCO₃ in 1 L water) is inoculated with approximately 10⁷CFU/mL of Staphylococcus aureus ATCC 6538, Enterobacter aerogenes ATCC13048, and Escherichia coli ATCC 8739. Aliquots of the cell suspensionare then treated with THPS, BIT, and combinations of these actives atselected concentrations and incubated at 37° C. for 14 days. Afterincubation for 24 hours, 3 days, and 7 days, the aliquots arere-challenged with bacterial suspension of the same bacteria at a finalbacterial concentration of 10⁵ CFU/mL. The biocidal efficacy is measuredat 2 hours and 14 days by determining the minimum biocide concentrationfor 99.9% bacterial kill in the aliquots. Synergy Index is thencalculated. Table 1 and 2 summarize the efficacy of each biocide andtheir combinations at 2 hour and 14 day treatment time respectively, andthe resulting Synergy Index of each combination.

TABLE 1 Biocidal efficacy of THPS, BIT, THPS/BIT combinations after 2hour treatment, and resulting Synergy Index. Concentration (ppm active)for 99.9% bacterial Active weight kill in 2 hours Synergy ratio ofTHPS:BIT THPS BIT Index 1:0 38 0 8:1 33 4 <0.90 4:1 30 8 <0.83 2:1 50 25<1.42 1:2 >100 >200 NA 1:4 >60 >240 NA 1:8 >33 >267 NA 0:1 >300

TABLE 2 Biocidal efficacy of THPS, BIT, THPS/BIT combinations after 14day treatment, and resulting Synergy Index Concentration (ppm active)for 99.9% bacterial Active weight kill in 14 days Synergy ratio ofTHPS:BIT THPS BIT Index 1:0 >300 8:1 267 33 <1.11 4:1 240 60 <1.20 2:1200 100 <1.33 1:2 50 100 <0.67 1:4 30 120 <0.90 1:8 8 67 <0.47 0:1 150

As shown in Table 1 and Table 2, THPS in combination with BIT hassynergistic effect against tested bacteria for both short term andextended treatment period.

Example 2 Synergistic Effect of Tetrakis (Hydroxymethyl) PhosphoniumSulfate (THPS) and 2-Methyl-1,2-Benzisothiazolin-3-One (MBIT)

Synergy tests of MBIT and THPS are conducted using standard 96 wellmicro titer plate assay with media design for the optimal growth of thetest microorganisms. For yeast (Candida albican, ATCC #10231) testing,SDB (Sabouraud Dextrose Broth) is used. The minimum inhibitoryconcentration (MIC) of biocides blends is performed by adding 170 uL ofSDB, 10 μl of tested organism and 10 μl of each biocides into the 64 ofthe 96 well plate. The final biocides and test inoculum concentrationsin each well are established based on this total volume. The final testinoculums concentration are approximately 10⁴ cfu/ml. The highestconcentration of MBIT and THPS used in this synergy study is 10 and 4000ppm respectively. Eight subsequent 2 fold dilutions of each biocide areprepared using automated liquid handling system. The first biocide isadded into the well plate horizontally and the second biocide is addedafter rotating the plate 90 degrees. Columns nine and ten are reservedfor each individual biocide to be tested at each concentration level toachieve an active inhibitory end point for synergy index calculation.Columns 11 and 12 are used as positive controls just containing mediaand the test organism. The plates are incubated at 25° C. for 48 hoursor until growth is observed in the control wells. Plates are scored asgrowth or no growth based on turbidity formation and the lowest passingconcentration is recorded.

Ratios of the two biocides exhibiting synergy are presented in Table 3.Synergy of MBIT and THPS against E. coli and Aspergillus niger was notobserved at the tested ratios.

TABLE 3 Active Minimum Inhibitory Weight Concentration ratio against ofMBIT Candida albican and (ppm) Synergy THPS MBIT THPS Index 1:0 0.3750:1 1000 1:5,000 0.1 500 0.77 1:10,000 0.05 500 0.63

What is claimed is:
 1. A composition comprising2-methyl-1,2-benzisothiazolin-3-one and tetrakis (hydroxymethyl)phosphonium sulfate and in a weight ration form 1:5000 to 1:10000.
 2. Amethod for controlling microorganisms in an aqueous or water-containingsystem, the method comprising treating the system with the compositionof claim
 1. 3. The method of claim 2 wherein the aqueous orwater-containing system is used or is present in oil or gas production.4. The method of claim 3 wherein oil or gas production comprisesinjection and produced water, source water for waterflooding andhydraulic fracturing, pond water, holding tank water, functional fluids,drilling muds, completion and workover fluids, hydrotest fluids,stimulation fluids, packer fluids, fracturing fluids, oil and gas wells,separation, storage and transportation systems, oil and gas pipelines,oil and gas vessels, or fuel.
 5. The method of claim 2 wherein theaqueous or water-containing system is cooling water, air washer, heatexchangers, boiler water, pulp and paper mill water, other industrialprocess water, ballast water, wastewater, metalworking fluids, latex,paint, coatings, adhesives, inks, tape joint compounds, pigment,water-based slurries, swimming pool, personal care and householdproducts such as detergent, membrane and filtration systems, toiletbowel, textiles, leather and leather production system, or a system usedtherewith.
 6. The method of claim 2 wherein the microorganisms areanaerobic bacteria.
 7. The method of claim 2 wherein the microorganismsare aerobic bacteria.